Coated substrates

ABSTRACT

A coated substrate, especially a glass substrate, such coated substrate having high photocatalytic activity and low visible light reflection as well as being highly abrasion resistant. Preferably, the coating is a titanium oxide coating, the photolytic activity is greater than 5×10 −3  cm −1 min −1 , and coating side visible light reflection is 35% or lower.

RELATED APPLICATION

This application is a continuation application of U.S. Ser. No.10/144,010, filed May 13, 2002, which is pending as of the filing dateof the present application, and which is a divisional application ofapplication Ser. No. 09/587,970, filed Jun. 6, 2000, and which has sinceissued as U.S. Pat. No. 6,840,061. U.S. Pat. No. 6,840,061 and U.S.application Ser. No. 10/144,010 are hereby incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

This invention relates to photocatalytically active coated substrates,in particular, but not exclusively, it relates to a photocatalyticallyactive coated glass.

It is known to deposit thin coatings having one or more layers, with avariety of properties, on to substrates including on to glasssubstrates. One property of interest is photocatalytic activity whicharises by the photogeneration, in a semiconductor, of a hole-electronpair when the semiconductor is illuminated by light of a particularfrequency. The hole-electron pair can be generated in sunlight and canreact in humid air to form hydroxy and peroxy radicals on the surface ofthe semiconductor. The radicals oxidise organic grime on the surface.This property has an application in self-cleaning substrates, especiallyin self-cleaning glass for windows.

Titanium dioxide may be an efficient photocatalyst and may be depositedon to substrates to form a transparent coating with photocatalyticself-cleaning properties. Titanium oxide photocatalytic coatings aredisclosed in EP 0 901 991 A2, WO 97/07069, WO 97/10186, WO 98/41480, inAbstract 735 of 187th Electrochemical Society Meeting (Reno, NV, 95-1,p. 1102) and in New Scientist magazine (26 Aug. 1995, p. 19). In WO98/06675 a chemical vapor deposition process is described for depositingtitanium oxide coatings on hot flat glass at high deposition rate usinga precursor gas mixture of titanium chloride and an organic compound assource of oxygen for formation of the titanium oxide coating.

It has been thought that relatively thick titanium oxide coatings needto be deposited to provide good photocatalytic activity. For example, inWO 98/41480 it is stated that a photocatalytically active self-cleaningcoating must be sufficiently thick so as to provide an acceptable levelof activity and it is preferred that such a coating is at least about200 Å and more preferably at least about 500 Å thick (the measuredthickness of the titanium oxide coatings produced in the Examples allbeing in the range 400 Å to 2100 Å).

However, a problem of relatively thick titanium oxide coatings is highvisible light reflection and thus relatively low visible lighttransmission. This problem is recognized in the article in New Scientistmagazine in relation to coated windscreens, where it is suggested thatto reduce the effect of high reflection, dashboards might have to becoated in black velvet or some other material that does not reflectlight into a coated windscreen.

EP 0 901 991A2 referred to above relates to photocatalytic glass paneswith a coating of titanium oxide of a particular crystal structurecharacterised by the presence of particular peaks in its X-raydiffraction pattern. The specification contemplates a range of coatingthickness (with the specific Examples all having thickness in the range20 nm to 135 nm, the thinner coatings being less photocatalyticallyactive than the thicker coatings). The specification also contemplates arange of deposition temperatures from as low as 300° C. to as high as750° C., but prefers temperatures in the range 400° C. to 600° C., andin all the specific Examples of the invention the titanium dioxide layeris deposited at a temperature in or below this preferred range.

The applicants have now found that by depositing the titanium oxidecoatings at higher temperatures, especially temperatures above 600° C.,they are able to achieve coatings with an enhanced photocatalyticactivity for a given thickness, enabling the same photocatalyticperformance to be achieved with thinner coatings. Such thinner coatingstend to have, advantageously, lower visible light reflection and,apparently in consequence of their higher deposition temperature,improved durability, especially to abrasion and temperature cycling in ahumid atmosphere.

SUMMARY OF THE INVENTION

The present invention accordingly provides a process for the productionof a photocatalytically active coated substrate which comprisesdepositing a titanium oxide coating on the surface of a substrate bycontacting the surface of the substrate with a fluid mixture containinga source of titanium and a source of oxygen, said substrate being at atemperature of at least 600° C., whereby the coated surface of thesubstrate has a photocatalytic activity of greater than 5×10⁻³ cm⁻¹min⁻¹ and a visible light reflection measured on the coated side of 35%or lower.

Preferably, the substrate is at a temperature in the range 625° C. to720° C., more preferably the substrate is at a temperature in the range645° C. to 720° C.

Advantageously, the fluid mixture comprises titanium chloride as thesource of titanium and an ester other than a methyl ester. Thus, in apreferred embodiment, the present invention provides a process for theproduction of a photocatalytically active coated substrate whichcomprises depositing a titanium oxide coating having a thickness of lessthan 40 nm on a substrate by contacting a surface of the substrate witha fluid mixture comprising titanium chloride and an ester other than amethyl ester.

The process may be performed wherein the surface of the substrate iscontacted with the fluid mixture when the substrate is at a temperaturein the range 600° C. to 750° C.

Preferably, the ester is an alkyl ester having an alkyl group with a βhydrogen (the alkyl group of an alkyl ester is the group derived fromthe alcohol in synthesis of an ester and a β hydrogen is a hydrogenbonded to a carbon atom β to the oxygen of the ether linkage in anester). Preferably the ester is a carboxylate ester.

Suitable esters may be alkyl esters having a C₂ to C₁₀ alkyl group, butpreferably the ester is an alkyl ester having a C₂ to C₄ alkyl group.

Preferably, the ester is a compound of formula:R—C(O)—O—C(X)(X′)—C(Y)(Y′)—R′, where R and R′ represent hydrogen or analkyl group, X, X′, Y and Y′ represent monovalent substituents,preferably alkyl groups or hydrogen atoms and wherein at least one of Yand Y′ represents hydrogen.

Suitable esters that may be used in the process of the present inventioninclude: ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate,n-propyl formate, n-propyl acetate, n-propyl propionate, n-propylbutyrate, isopropyl formate, isopropyl acetate, isopropyl propionate,isopropyl butyrate, n-butyl formate, n-butyl acetate and t-butylacetate.

Preferably, the ester comprises an ethyl ester, more preferably theester comprises ethyl formate, ethyl acetate or ethyl propionate. Mostpreferably the ester comprises ethyl acetate.

The fluid mixture may be in the form of a liquid, especially dispersedas a fine spray (a process often referred to as spray deposition), butpreferably the fluid mixture is a gaseous mixture. A deposition processperformed using a gaseous mixture as precursor is often referred to aschemical vapor deposition (CVD). The preferred form of CVD is laminarflow CVD, although turbulent flow CVD may also be used.

The process may be performed on substrates of various dimensionsincluding on sheet substrates, especially on cut sheets of glass, orpreferably on-line during the float glass production process on acontinuous ribbon of glass. Thus, preferably, the process is performedon-line during the float glass production process and the substrate is aglass ribbon. If the process is performed on line, it is preferablyperformed on the glass ribbon whilst it is in the float bath.

An advantage of performing the process on-line is that coatingsdeposited on-line tend to be durable and in particular to have goodabrasion and chemical resistance.

An on-line deposition process is preferably, and other depositionprocesses may be, performed at substantially atmospheric pressure.

In a particularly preferred embodiment there is provided a process forthe production of a durable photocatalytically active coated glass whichcomprises depositing on the surface of a glass substrate aphotocatalytically active titanium oxide layer by contacting the surfaceof the substrate, which is at a temperature in the range 645° C. to 720°C., preferably in the range 670° C. to 720° C. with a fluid mixturecontaining a source of titanium.

As noted above, the applicants have found that by depositing thetitanium oxide at high temperature, a coating of relatively highphotocatalytic activity for its thickness may be produced and, ascoatings of reduced thickness tend to have lower reflection, theinvention also provides novel products having an advantageouscombination of high photocatalytic activity with moderate or low lightreflection.

Thus, the present invention, in another aspect, provides aphotocatalytically active coated substrate comprising a substrate havinga photocatalytically active titanium oxide coating on one surfacethereof, characterised in that the coated surface of the substrate has aphotocatalytic activity of greater than 5×10⁻³ cm⁻¹min⁻¹ and in that thecoated substrate has a visible light reflection measured on the coatedside of 35% or lower.

High photocatalytic activity is advantageous because the amount ofcontaminants (including dirt) on the coated surface of thephotocatalytically active coated substrate will be reduced quicker thanon substrates with relatively low photocatalytic activity. Also,relatively quick removal of surface contaminants will tend to occur atlow levels of UV light intensity.

Photocatalytic activity for the purposes of this specification isdetermined by measuring the rate of decrease of the integratedabsorbance of the infra-red absorption peaks corresponding to the C—Hstretches of a thin film of stearic acid, formed on the coatedsubstrate, under illumination by UV light from a UVA lamp having anintensity of about 32 W/m² at the surface of the coated substrate and apeak wavelength of 351 nm. The stearic acid may be formed on the coatedsubstrate by spin casting a solution of stearic acid in methanol asdescribed below.

Preferably, the coated surface of the substrate has a photocatalyticactivity of greater than 1×10⁻² cm⁻¹min⁻¹, more preferably of greaterthan 3×10⁻² cm⁻¹min⁻¹.

Low visible light reflection is advantageous because it is lessdistracting than high reflection and, especially for glass substrates,low visible light reflection corresponds to high visible transmissionwhich is often required in architectural and especially automotiveapplications of glass.

Preferably, the coated substrate has a visible reflection measured onthe coated side of 20% or lower more preferably of 17% or lower and mostpreferably of 15% or lower.

In most embodiments of the invention the substrate will be substantiallytransparent and in a preferred embodiment of the invention the substratecomprises a glass substrate. Usually the glass substrate will be a sodalime glass substrate.

Where the substrate is a soda lime glass substrate or other alkali metalion containing substrate, the coated substrate preferably has an alkalimetal ion blocking under layer between the surface of the substrate andthe photocatalytically active titanium oxide coating. This reduces thetendency for alkali metal ions from the substrate to migrate into thephotocatalytically active titanium oxide coating which is advantageousbecause of the well known tendency of alkali metal ions to poisonsemiconductor oxide coatings, reducing their activity.

The alkali metal ion blocking under layer may comprise a metal oxide butpreferably the alkali metal ion blocking layer is a layer of siliconoxide. The silicon oxide may be silica but will not necessarily bestoichiometric and may comprise impurities such as carbon (oftenreferred to as silicon oxycarbide and deposited as described in GB2,199,848B) or nitrogen (often referred to as silicon oxynitride).

It is advantageous if the alkali metal ion blocking under layer is thinso that it has no significant effect on the optical properties of thecoating, especially by reducing the transparency of a transparent coatedsubstrate or causing interference colors in reflection or transmission.The suitable thickness range will depend on the properties of thematerial used to form the alkali metal ion blocking layer (especiallyits refractive index), but usually the alkali metal ion blocking underlayer has a thickness of less than 60 nm and preferably has a thicknessof less than 40 nm. Where present, the alkali metal ion blocking underlayer should always be thick enough to reduce or block migration ofalkali metal ions from the glass into the titanium oxide coating.

An advantage of the present invention is that the photocatalyticallyactive titanium oxide coating is thin (contributing to the low visiblereflection of the coated substrate) but the coated substrate still hasexcellent photocatalytic activity. Preferably, the titanium oxidecoating has a thickness of 30 nm or lower, more preferably the titaniumoxide coating has a thickness of 20 nm or lower and most preferably thetitanium oxide coating has a thickness in the range 2 nm to about 20 nm.

The present invention is also advantageous because depositing thintitanium oxide coatings requires less precursor and the layers can bedeposited in a relatively short time. A thin titanium oxide coating isalso less likely to cause interference colors in reflection ortransmission. However, a particular advantage is that the visible lightreflection of a thin titanium oxide coating is low which is especiallyimportant when the coated substrate is coated glass. Usually therequired visible light transmission of the coated glass will determinethe thickness of the titanium oxide coating.

Preferably, the coated surface of the substrate has a static watercontact angle of 20° or lower. Freshly prepared or cleaned glass has ahydrophilic surface (a static water contact angle of lower than about40° indicates a hydrophilic surface), but organic contaminants rapidlyadhere to the surface increasing the contact angle. A particular benefitof coated substrates (and especially coated glasses) of the presentinvention is that even if the coated surface is soiled, irradiation ofthe coated surface by UV light of the right wavelength will reduce thecontact angle by reducing or destroying those contaminants. A furtheradvantage is that water will spread out over the low contact anglesurface reducing the distracting effect of droplets of water on thesurface (e.g. from rain) and tending to wash away any grime or othercontaminants that have not been destroyed by the photocatalytic activityof the surface. The static water contact angle is the angle subtended bythe meniscus of a water droplet on a glass surface and may be determinedin a known manner by measuring the diameter of a water droplet of knownvolume on a glass surface and calculated using an iterative procedure.

Preferably, the coated substrate has a haze of 1% or lower, which isbeneficial because this allows clarity of view through a transparentcoated substrate.

In preferred embodiments, the coated surface of the substrate is durableto abrasion, such that the coated surface remains photocatalyticallyactive after it has been subjected to 300 strokes of the Europeanstandard abrasion test. Preferably, the coated surface remainsphotocatalytically active after it has been subjected to 500 strokes ofthe European standard abrasion test, and more preferably the coatedsurface remains photocatalytically active after it has been subjected to1000 strokes of the European standard abrasion test.

This is advantageous because self-cleaning coated substrates of thepresent invention will often be used with the coated surface exposed tothe outside (e.g. coated glasses with the coated surface of the glass asthe outer surface of a window) where the coating is vulnerable toabrasion.

The European standard abrasion test refers to the abrasion testdescribed in European standard BS EN 1096 Part 2 (1999) and comprisesthe reciprocation of a felt pad at a set speed and pressure over thesurface of the sample.

In the present specification, a coated substrate is considered to remainphotocatalytically active if, after being subjected to the Europeanabrasion test, irradiation by UV light (e.g. of peak wavelength 351 nm)reduces the static water contact angle to below 15°. To achieve thiscontact angle after abrasion of the coated substrate will usually takeless than 48 hours of irradiation at an intensity of about 32 W/m² atthe surface of the coated substrate.

Preferably, the haze of the coated substrate is 2% or lower after beingsubjected to the European standard abrasion test.

Durable coated substrates according to the present invention may also bedurable to humidity cycling (which is intended to have a similar effectto weathering). Thus, in preferred embodiments of the invention, thecoated surface of the substrate is durable to humidity cycling such thatthe coated surface remains photocatalytically active after the coatedsubstrate has been subjected to 200 cycles of the humidity cycling test.In the present specification, the humidity cycling test refers to a testwherein the coating is subjected to a temperature cycle of 35° C. to 75°C. to 35° C. in 4 hours at near 100% relative humidity. The coatedsubstrate is considered to remain photocatalytically active, if, afterthe test, irradiation by UV light reduces the static water contact angleto below 15°.

In a further preferred embodiment, the present invention provides adurable photocatalytically active coated glass comprising a glasssubstrate having a coating on one surface thereof, said coatingcomprising an alkali metal ion blocking under layer and aphotocatalytically active titanium oxide layer, wherein the coatedsurface of the substrate is durable to abrasion such that the coatedsurface remains photocatalytically active after it has been subjected to300 strokes of the European standard abrasion test. In this embodiment,the coated glass preferably has a visible light reflection measured onthe coated side of 35% or lower, and the photocatalytically activetitanium oxide layer preferably has a thickness of 30 nm or lower. Thincoatings are durable to abrasion which is surprising because previouslyit has been thought that only relatively thick coatings would have gooddurability.

In a still further embodiment, the present invention provides a coatedglass comprising a glass substrate having a photocatalytically activetitanium oxide coating on one surface thereof, characterised in that thecoated surface of the glass has a photocatalytic activity of greaterthan 4×10⁻² cm⁻¹min⁻¹, preferably greater than 6×10⁻² cm⁻¹min⁻¹ and morepreferably greater than 8×10⁻² cm⁻¹min⁻¹ and in that the coated glasshas a visible light reflection measured on the coated side of less than20%.

Coated substrates according to the present invention have uses in manyareas, for example as glazing in windows including in a multiple glazingunit comprising a first glazing pane of a coated substrate in spacedopposed relationship to a second glazing pane, or, when the coatedsubstrate is coated glass, as laminated glass comprising a first glassply of the coated glass, a polymer interlayer (of, for example,polyvinylbutyral) and a second glass ply.

In addition to uses in self-cleaning substrates (especiallyself-cleaning glass for windows), coated substrates of the presentinvention may also be useful in reducing the concentration ofatmospheric contaminants. For example, coated glass under irradiation bylight of UV wavelengths (including UV wavelengths present in sunlight)may destroy atmospheric contaminants for example, nitrogen oxides, ozoneand organic pollutants, adsorbed on the coated surface of the glass.This use is particularly advantageous in the open in built-up areas (forexample, in city streets) where the concentration of organiccontaminants may be relatively high (especially in intense sunlight),but where the available surface area of glass is also relatively high.Alternatively, the coated glass (with the coated surface on the inside)may be used to reduce the concentration of atmospheric contaminantsinside buildings, especially in office buildings having a relativelyhigh concentration of atmospheric contaminants.

The invention is illustrated but not limited by the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of photocatalytic activity of coated glass produced bya process according to the invention as a function of the thickness ofthe titanium oxide layer.

FIG. 2 illustrates apparatus for on line chemical vapor deposition ofcoatings according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 the coated glasses were produced using an on-line CVD processas described in the Examples, below. The open circles 1 relate totitanium oxide layers deposited using titanium tetrachloride as titaniumprecursor, and the crosses 2 relate to titanium oxide layers depositedusing titanium tetraethoxide as titanium precursor.

The layers of the coating may be applied on line onto the glasssubstrate by chemical vapor deposition during the glass manufacturingprocess. FIG. 2 illustrates an apparatus, indicated generally at 10,useful for the on line production of the coated glass article of thepresent invention, comprising a float section 11, a lehr 12, and acooling section 13. The float section 11 has a bottom 14 which containsa molten tin bath 15, a roof 16, sidewalls (not shown), and end walls17, which together form a seal such that there is provided an enclosedzone 18, wherein a non-oxidizing atmosphere is maintained to preventoxidation of the tin bath 15. During operation of the apparatus 10,molten glass 19 is cast onto a hearth 20, and flows there from under ametering wall 21, then downwardly onto the surface of the tin bath 15,forming a float glass ribbon 37, which is removed by lift-out rolls 22and conveyed through the lehr 12, and thereafter through the coolingsection 13.

A non-oxidizing atmosphere is maintained in the float section 11 byintroducing a suitable gas, such as for example one comprising nitrogenand 2% by volume hydrogen, into the zone 18, through conduits 23 whichare operably connected to a manifold 24. The non-oxidizing gas isintroduced into the zone 18 from the conduits 23 at a rate sufficient tocompensate for losses of the gas (some of the non-oxidizing atmosphereleaves the zone 18 by flowing under the end walls 17), and to maintain aslight positive pressure above ambient pressure. The tin bath 15 and theenclosed zone 18 are heated by radiant heat directed downwardly fromheaters 25. The heat zone 18 is generally maintained at a temperature ofabout 1330° F. to 1400° F. (721° C. to 760° C.). The atmosphere in thelehr 12 is typically air, an the cooling section 13 is not enclosed.Ambient air is blown onto the glass by fans 26.

The apparatus 10 also includes coaters 27, 28, 29 and 30 located inseries in the float zone 11 above the float glass ribbon 37. Theprecursor gaseous mixtures for the individual layers of the coating aresupplied to the respective coaters, which in turn direct the precursorgaseous mixtures to the hot surface of the float glass ribbon 37. Thetemperature of the float glass ribbon 37 is highest at the location ofthe coater 27 nearest the hearth 20 and lowest at the location of thecoater 30 nearest the lehr 12.

The invention is further illustrated by the following Examples, in whichcoatings were applied by laminar flow chemical vapor deposition in thefloat bath on to a moving ribbon of float glass during the glassproduction process. In the Examples two layer coatings were applied tothe glass ribbon.

All gas volumes are measured at standard temperature and pressure unlessotherwise stated. The thickness values quoted for the layers weredetermined using high resolution scanning electron microscopy andoptical modelling of the reflection and transmission spectra of thecoated glass. Thickness of the coatings was measured with an uncertaintyof about 5%. The transmission and reflection properties of the coatedglasses were determined using a Hitachi U—4000 spectrophotometer. The a,b and L* values mentioned herein of the transmission and/or reflectioncolor of the glasses refer to the CIE Lab colors. The visible reflectionand visible transmission of the coated glasses were determined using theD65 illuminant and the standard CIE 2° observer in accordance with theISO 9050 standard (Parry Moon airmass 2). The haze of the coated glasseswas measured using a WYK− Gardner Hazeguard+ haze meter.

The photocatalytic activity of the coated glasses was determined fromthe rate of decrease of the area of the infrared peaks corresponding toC—H stretches of a stearic acid film on the coated surface of the glassunder illumination by UVA light. The stearic acid film was formed onsamples of the glasses, 7-8 cm square, by spin casting 20 μl of asolution of stearic acid in methanol (8.8×10⁻³ mol dm⁻³) on the coatedsurface of the glass at 2000 rpm for 1 minute. Infra red spectra weremeasured in transmission, and the peak height of the peak correspondingto the C—H stretches (at about 2700 to 3000 cm⁻¹) of the stearic acidfilm was measured and the corresponding peak area determined from acalibration curve of peak area against peak height. The coated side ofthe glass was illuminated with a UVA-351 lamp (obtained from the Q-PanelCo., Cleveland, Ohio, USA) having a peak wavelength of 351 nm and anintensity at the surface of the coated glass of approximately 32 W/m².The photocatalytic activity is expressed in this specification either asthe rate of decrease of the area of the IR peaks (in units of cm⁻¹min⁻¹) or as t_(90%) (in units of min) which is the time of UV exposuretaken to reduce the peak height (absorption) of a peak in the wavelengtharea down to 10% of its initial value.

The static water contact angle of the coated glasses was determined bymeasuring the diameter of a water droplet (volume in the range 1 to 5μl) placed on the surface of the coated glass after irradiation of thecoated glass using the UVA 351 lamp for about 2 hours (or as otherwisespecified).

EXAMPLES 1-15

A ribbon of 1 mm thick soda lime float glass advancing at a lehr speedof 300 m/hour was coated with a two-layer coating as the ribbon advancedover the float bath at a position where the glass temperature was in therange of about 650° C. to about 670° C. The float bath atmospherecomprised a flowing gaseous mixture of nitrogen and 9% hydrogen at abath pressure of approximately 0.15 mbar.

Layer 1 (the first layer to be deposited on the glass) was a layer ofsilicon oxide. Layer 1 was deposited by causing a gaseous mixture ofmonosilane (SiH₄, 60 ml/min), oxygen (120 ml/min), ethylene (360 ml/min)and nitrogen (8 litres/min) to contact and flow parallel to the glasssurface in the direction of movement of the glass using coatingapparatus as described in GB patent specification 1 507 966 (referringin particular to FIG. 2 and the corresponding description on page 3 line73 to page 4 line 75) with a path of travel of the gaseous mixture overthe glass surface of approximately 0.15 m. Extraction was atapproximately 0.9 to 1.2 mbar. The glass ribbon was coated across awidth of approximately 10 cm at a point where its temperature wasapproximately 670° C. The thickness of the silica layer was about 20 to25 m.

Layer 2 (the second layer to be deposited) was a layer of titaniumdioxide. Layer 2 was deposited by combining separate gas streamscomprising titanium tetrachloride in flowing nitrogen carrier gas, ethylacetate in flowing nitrogen carrier gas and a bulk flow of nitrogen of 8l/min (flow rate measured at 20 psi) into a gaseous mixture and thendelivering (through lines maintained at about 250° C.) the gaseousmixture to coating apparatus consisting of an oil cooled dual flowcoater. The pressure of the nitrogen carrier and bulk nitrogen gases wasapproximately 20 pounds per square inch. The gaseous mixture contactedand flowed parallel to the glass surface both upstream and downstreamalong the glass ribbon. The path of travel of the gaseous mixturedownstream was about 0.15 m and upstream was about 0.15 m withextraction of about 0.15 mbar. Titanium tetrachloride and ethyl acetatewere entrained in separate streams of flowing nitrogen carrier gas bypassing nitrogen through bubblers containing either titaniumtetrachloride or ethyl acetate. The flow rates of the nitrogen carriergases are described in Table 1 (the flow rates were measured at 20 psi).The titanium tetrachloride bubbler was maintained at a temperature of69° C. and the ethyl acetate bubbler was maintained at a temperature of42° C. The estimated flow rates of entrained titanium tetrachloride andentrained ethyl acetate are also described in Table 1 for each of theExamples 1 to 15.

The properties of the two-layer coatings were measured. Values of thethickness of layer 2 (the titanium oxide layer), and values of thevisible reflection measured on the coated side, L* and haze of thecoated glasses are described in Table 2 for the Examples 1-15. The hazeof each coated glass was below 0.2%.

The photocatalytic activity and static water contact angle of the coatedglasses were determined. The initial peak height and initial peak areaof the IR peaks corresponding to the stearic acid C—H stretches, thephotocatalytic activity, the static water contact angle and t_(90%) forthe Examples 1-15 are described in Table 3. The thickness of thetitanium oxide layer, surprisingly has little effect on photocatalyticactivity.

EXAMPLES 16-19

Examples 16-19 were conducted under the same conditions as Examples 1-15except that the bath pressure was approximately 0.11 mbar, extractionfor deposition of the silica undercoat (layer 1) was approximately 0.7mbar, the titanium tetrachloride bubbler was maintained at a temperatureof approximately 100° C., the ethyl acetate bubbler was maintained at atemperature of approximately 45° C. and the delivery lines weremaintained at a temperature of approximately 220° C.

The flow rates of nitrogen carrier gas, and the estimated flow rates ofentrained titanium tetrachloride and entrained ethyl acetate aredisclosed for each of the examples 16-19 in Table 1.

Values of the estimated thickness of layer 2 (the titanium oxide layer),and values of visible reflection measured on the coated side, L* andhaze of the coated glasses are described in Table 2 for each of theExamples 16-19.

The initial peak height and initial peak area of the IR peakscorresponding to the stearic acid C—H stretches, the photocatalyticactivity, t_(90%) and the static water contact angle and for each of theExamples 16-19 are described in Table 3.

The photocatalytic activity of the Examples 16-19 was not substantiallygreater than that of the Examples 1-15 despite the thicker titaniumoxide (and hence more reflective) coatings. TABLE 1 Nitrogen Carrier GasFlow Rates to Bubblers Ethyl (l/min, measured at 20 psi) Acetate EthylAcetate TiCl₄ flow rate flow rate Example TiCl₄ Bubbler Bubbler (l/min)(l/min) 1 0.16 1 0.032 0.46 2 0.12 0.3 0.024 0.14 3 0.12 0.45 0.024 0.214 0.08 0.2 0.016 0.09 5 0.12 0.15 0.024 0.07 6 0.12 0.75 0.024 0.35 70.08 0.3 0.016 0.14 8 0.08 0.5 0.016 0.23 9 0.04 0.1 0.008 0.05 10 0.040.15 0.008 0.07 11 0.04 0.25 0.008 0.12 12 0.16 0.1 0.032 0.05 13 0.080.1 0.016 0.05 14 0.16 0.4 0.032 0.19 15 0.16 0.2 0.032 0.09 16 0.1 0.50.088 0.27 17 0.08 0.4 0.070 0.22 18 0.06 0.3 0.053 0.16 19 0.04 0.20.035 0.11

TABLE 2 Thickness of titanium oxide L* value of layer Visible reflectionof coated glass Haze Example (nm) coated glass (%) (%) (%) 1 15 14.1 440.12 2 14.3 13.9 44 0.07 3 14.2 13.2 43 0.12 4 11.3 11.4 40 0.08 5 12.112.1 41 0.08 6 11.0 a a 0.07 7 8 A a 0.11 8 7.2 9.7 37 0.04 9 6.1 9.1 360.05 10 5.6 9 36 0.07 11 4.6 8.7 35 0.06 12 15.6 15.4 46 0.1 13 16.0 A a0.13 14 17.5 16.2 47 0.14 15 20.3 19.5 51 0.1 16 a 28.4 47.8 0.3 17 ca68 29.1 58.4 0.37 18 ca 32 25.9 55.6 0.24 19 ca 27 20.5 50.2 0.2a Not measured

TABLE 3 IR Peaks corresponding to stearic acid film C—H Static stretches(2700-3000 cm⁻¹) Photocatalytic Water Initial Peak Activity ContactExam- Height Initial Peak (×10⁻² cm⁻¹ Angle t_(90%) ple (arbitraryunits) Area (cm⁻¹) min⁻¹) (°) (min) 1 0.030 1.04 9.4 17 ± 5 10 2 0.03311.15 10.4 15 ± 1 10 3 0.0311 1.08 12.2 13 ± 2 8 4 0.0324 1.13 6.8 14 ± 115 5 0.0287 1.00 8.2 16 ± 3 11 6 0.028 0.98 8.8 15 ± 1 10 7 0.0343 1.2010.8 15 ± 1 10 8 0.0289 1.03 6.6 16 ± 1 14 9 0.0289 1.01 6.5 14 ± 2 1410 0.0278 0.97 6.2 18 ± 2 14 11 0.0344 1.20 5.4 18 ± 1 20 12 0.0291 1.0210.2 12 ± 1 9 13 0.0289 1.01 9.1 14 ± 2 10 14 0.0269 0.94 9.4 15 ± 2 915 0.0331 1.15 8.7 15 ± 2 12 16 0.0227 0.79 17.8 12 4 17 0.026 0.91 10.212 8 18 0.0225 0.79 10.1 13 7 19 0.0258 0.90 10.1 16 8

EXAMPLES 20-27

The Examples 20-27 were conducted under the same conditions as Examples1-15 except that layer 2 was deposited from a gaseous mixture comprisingtitanium tetraethoxide entrained in nitrogen carrier gas by passing thecarrier gas through a bubbler containing titanium tetraethoxidemaintained at a temperature of 170° C. The flow rates of nitrogencarrier gas (measured at 20 psi) and titanium tetraethoxide aredescribed in Table 4 for each of the Examples 20-27. The flow rate ofbulk nitrogen gas was 8.5 l/min (measured at 20 psi).

The properties of the two-layer coatings were measured. Values of thethickness of layer 2 (the titanium oxide layer), and values of thevisible reflection measured on the coated side and haze of the coatedglasses are described in Table 5 for the Examples 20-27. The haze ofeach coated glass was below 0.7%.

The photocatalytic activity and static water contact angle of the coatedglasses were determined. The initial peak height and initial peak areaof the IR peaks corresponding to the stearic acid C—H stretches, thephotocatalytic activity and t_(90%), and the static water contact anglefor each of the Examples 20-27 are described in Table 6.

EXAMPLES 28 and 29

The Examples 28 and 29 were conducted under the same conditions asExamples 20-27 except that the titanium tetraethoxide bubbler wasmaintained at a temperature of 168° C. and the bath pressure was 0.11mbar. Data relating to Examples 28-29 equivalent to data for Examples20-27 are described in Tables 4, 5 and 6. TABLE 4 Nitrogen Carrier GasFlow Rates to Titanium tetraethoxide Titanium ethoxide flow bubbler(l/min, rate Example measured at 20 psi) (l/min) 20 0.25 0.014 21 0.150.008 22 0.2 0.011 23 0.25 0.014 24 0.3 0.017 25 0.35 0.019 26 0.2 0.01127 0.1 0.006 28 0.6 0.030 29 0.4 0.020

TABLE 5 Thickness of titanium oxide layer Visible reflection of HazeExample (nm) coated glass (%) (%) 20 13 a 0.4  21 13 a 0.29 22 16 15.70.29 23 18 a 0.28 24 24 a a 25 26 a 0.61 26 9.9 10.9 0.19 27 4.7  8.80.29 28 38.3 35.2 0.29 29 31.9 28.4 0.22a Not measured

TABLE 6 IR Peaks corresponding to stearic acid film C—H stretches(2700-3000 cm⁻¹) Initial Peak Photocatalytic Static Height ActivityWater Exam- (arbitrary Initial Peak (×10⁻² cm⁻¹ Contact t_(90%) pleunits) Area (cm⁻¹) min⁻¹) Angle (°) (min) 20 0.027 0.953 5.7 19 ± 5 1521 0.031 1.095 5.7 a 17 22 0.024 0.838 3.6 15 ± 2 21 23 0.030 1.029 7.111 ± 3 13 24 0.029 1.015 7 17 ± 3 13 25 0.031 1.071 7.4 13 ± 4 13 260.031 1.085 4.4 21 ± 3 22 27 0.029 0.998 3.2 16 ± 5 28 28 0.021 0.7333.6 13 18 29 0.024 0.848 3.3 14 23a Not measured

EXAMPLES 30-42

In Examples 30 to 42, two-layer coatings were applied by on line CVD toa float glass ribbon across its full width of approximately 132 inches(3.35 m) in the float bath during the float glass production process.The apparatus used to deposit the coating is illustrated in FIG. 2. Thefloat bath atmosphere comprised nitrogen and 2% by volume hydrogen. Bathpressure was 0.15 mbar.

The two layer coating consisted of a silicon oxide layer deposited firston the float glass ribbon and titanium oxide layer deposited on to thesilicon oxide layer. The precursor chemistry of the gaseous mixturesused to deposit the coating was the same as that used in Examples 1-15.The temperature of deposition of the layers was varied by usingdifferent coaters 27, 28, 29, or 30 (referring to FIG. 2). Coater 27located nearest the hearth being hottest and coater 30 located nearestthe lehr being coolest. In Examples 30-33 and 42 two coaters (28 and 29in Examples 30-33 and coaters 27 and 28 in Example 42) were used todeposit the silicon oxide coating. The benefit of using two coaters todeposit the silicon oxide layer is that longer production run times arepossible.

The gaseous mixture used to deposit the silicon oxide layer for Examples30 to 41 consisted of the following gases at the following flow rates:helium (250 l/min), nitrogen (285 l/min), monosilane (2.5 l/min),ethylene (15 l/min) and oxygen (10 l/min). For Example 42, the samegases and flow rates were used except for monosilane (2.3 l/min),ethylene (13.8 l/min) and oxygen (9.2 l/min). Where two coaters wereused to deposit the silicon oxide layer in Examples 30 to 42, the aboveflow rates were used for each coater.

In Examples 30-42 the deposition temperatures (i.e. the temperature ofthe float glass ribbon under the coater corresponding to each of thecoaters 27-30) was as indicated in Table 7. The temperatures in Table 7have an uncertainty of about ±50° F. (±28° C.). The extraction for eachcoater was at approximately 2 mbar. TABLE 7 Coater Approx. Temperatureof Glass Ribbon 27 1330° F. (721° C.) 28 1275° F. (690° C.) 29 1250° F.(677° C.) 30 1150° F. (621° C.)

Titanium tetrachloride (TiCl₄) and ethyl acetate were entrained inseparate nitrogen/helium carrier gas streams. For the evaporation ofTiCl₄ a thin film evaporator was used. The liquid TiCl₄ was held in apressurised container (head pressure approx 5 psi). This was used todeliver the liquid to a metering pump and Coriolis force flowmeasurement system. The metered flow of the precursor was then fed intoa thin film evaporator at a temperature of 110° F. (43° C.). The TiCl₄was then entrained in the carrier gas (helium) and delivered to themixing point down lines held at 250° F. (121° C.). The ethyl acetate wasdelivered in a similar way. The liquid ethyl acetate was held in apressurised container (head pressure approx 5 psi). This was used todeliver the liquid to a metering pump and Coriolis force flowmeasurement system. The metered flow of the precursor was then fed intoa thin film evaporator at a temperature of 268° F. (131° C.). Theevaporated ethyl acetate was then entrained in the carrier gas(helium/nitrogen mixture) and delivered to the mixing point down linesheld at approximately 250° F. (121° C.).

The TiCl₄ and ethyl acetate gas streams were combined to form thegaseous mixture used to deposit the titanium oxide layer. This mixingpoint was just prior to the coater.

The line speed of the float glass ribbon, the temperature of depositionof the silicon oxide and temperature of deposition of the titanium oxidelayers and the flow rates of the He/N₂ bulk carrier gas and the flowrate of TiCl₄ and ethyl acetate are described for Examples 30-42 inTable 8.

The coated float glass ribbon was cooled and cut and the opticalproperties and photocatalytic activity of samples determined. Table 9describes the haze, optical properties in transmission and reflection(visible percent transmission/reflection and color co-ordinates usingthe LAB system) of the samples. The coated glasses were subjected toabrasion testing in accordance with BS EN 1096, in which a sample ofsize 300 mm×300 mm is fixed rigidly, at the four corners, to the testbed ensuring that no movement of the sample is possible. An unused feltpad cut to the dimensions stated in the standard (BS EN 1096 Part 2(1999)) is then mounted in the test finger and the finger lowered to theglass surface. A load pressure on the test finger of 4N is then set andthe test started. The finger is allowed to reciprocate across the samplefor 500 strokes at a speed of 60 strokes/min±6 strokes/min. Uponcompletion of this abrasion the sample is removed and inspectedoptically and in terms of photocatalytic activity. The sample is deemedto have passed the test if the abrasion results in a change intransmission of no more than ±5% when measured at 550 nm and the coatedsubstrate remains photocatalytically active which means that, after thetest irradiation by UV light for 2 hours reduces the static watercontact angle to below 15°.

The glasses were also subjected to a humidity cycling test in which thecoating is subjected to a temperature cycle of 35° C. to 75° C. to 35°C. in 4 hours at near 100% relative humidity.

The static water contact angle of the coated glasses as produced andafter 130 minutes of UV irradiation (UVA 351 mm lamp at approximately 32W/m²) and after 300, 500 and/or 1000 strokes of the European standardabrasion test described in Table 10. The contact angle of the abradedsamples was determined after irradiation for 2 hours.

The samples deposited at the higher temperatures of 1330-1250° F. (721°C. to 677° C.) were photocatalytically active even after 1000 Europeanstandard abrasion strokes or after 200 humidity cycles. Thephotocatalytic activity in terms of t_(90%) of the coated glasses asproduced and after 300, 500 and/or 1000 strokes of the European standardabrasion test and after 200 humidity testing cycles are described inTable 11. In Table 11, the term Active indicates that the coated glasseswere photocatalytically active but that t_(90%) was not determined.

The photocatalytically active coated substrates of the invention havebeen illustrated and described in their preferred embodiments, however,it will be appreciated that modifications to these embodiments can bemade without departing from the spirit and scope of the attached claims.TABLE 8 Titanium Oxide Layer Line- Flow Rates of Flow Rates ofPrecursors Speed Silica layer Deposition Deposition Carrier Gases EthylAcetate Example (m/min) Temperature/° C. Temperature/° C. He L/min N₂L/min TiCl₄ cc/min cc/min 30 10.9 690 & 677 621 300 300 6.3 16.3 31 10.9690 & 677 621 300 300 6.3 16.3 32 10.9 690 & 677 621 300 300 6.3 16.3 3310.9 690 & 677 621 300 300 6.3 16.3 34 10.9 690 621 300 300 6 16 35 10.9690 621 300 300 6 16 36 10.9 690 621 300 300 6 16 37 10.9 690 677 300300 5.5 14.7 38 10.9 690 677 300 300 5.5 14.7 39 10.9 690 677 300 3005.5 14.7 40 10.9 690 677 300 300 5.5 14.7 41 6.5 721 690 300 300 4 10.742 12.1 721 & 690 677 300 300 9.5 25.4

TABLE 9 Exam- Film Side Reflection Transmission Haze ple R (%) L* a b T(%) L* a b (%) 30 14.2 44.5 0.3 −10.3  84.3 93.6 −1.2 3.6 0.11 31 14.645.1 0.3 −10.4  84.5 93.7 −1.1 3.4 0.30 32 14.6 45.1 0.3 −10.5  84.393.6 −1.1 3.6 0.12 33 13.8 44.0 0.3 −9.8 85.5 94.1 −1.1 2.9 0.15 34 13.643.7 0.1 −8.7 84.8 93.8 −1.1 2.7 0.12 35 13.8 43.9 0.1 −8.8 85.4 94.1−1.1 2.6 0.11 36 12.9 42.6 0.1 −8.2 85.8 94.2 −1.1 2.5 0.14 37 12.6 42.20.1 −7.9 86.1 94.4 −1.1 2.3 0.08 38 11.9 41.0 0.1 −6.9 87.1 94.8 −1.11.7 0.07 39 11.5 40.4 0.0 −6.5 87.2 94.8 −1.1 1.8 0.10 40 11.6 40.6 0.0−6.6 86.9 94.7 −1.1 1.8 0.08 41 a a a a a a a a a 42 14   44.3 0.1 −9.984.8 93.8 −1.1 3.1 0.14a Not Measure

TABLE 10 Static Water Contact Angle (°) after Number of Abrasion Strokes0 (after irradiation Example 0 130 min UV) 300 500 1000 30 2.3 3.3failed 31 2.0 3.2 failed 32 a a failed 33 2.0 3.2 failed 34 a a failed35 2.0 3.2 failed 36 2.1 3.4 failed 37 2.2 3.3 <15 38 2.0 3.1 <15 39 1.93.1 <15 40 2.2 3.2 <15 41 7.8 7.8 10.1 42 4.7-5.3 4.7-5.3 5.6-9.8a Not measured

TABLE 11 t_(90%) (min) after Number of Abrasion Strokes t_(90%) (min)after 200 Example 0 300 500 1000 Humidity Cycles 30 7.5 failed failed 3118.5 failed failed 32 8.5 failed failed 33 8 failed failed 34 21 failedfailed 35 4 failed failed 36 8.5 failed failed 37 15.5 Ca. 2160 Active38 18.5 Ca. 2160 Active 39 17 Ca. 2160 Active 40 18.5 Ca. 2160 Active 41a ca. 2160 Active 42 45 2800 Activea Not measured

1. A photocatalytically active coated substrate comprising a substratehaving a photocatalytically active titanium oxide coating on one surfacethereof, characterised in that the coated surface of the substrate has aphotocatalytic activity of greater than 5×10⁻³ cm⁻¹min⁻¹ and in that thecoated substrate has a visible light reflection measured on the coatedside of 35% or lower.
 2. A photocatalytically active coated substrate asclaimed in claim 1 wherein the coated surface of the substrate has aphotocatalytic activity of greater than 1×10⁻² cm⁻¹min⁻¹.
 3. Aphotocatalytically active coated substrate as claimed in claim 2 whereinthe coated surface of the substrate has a photocatalytic activity ofgreater than 3×10⁻² cm⁻¹min⁻¹.
 4. (canceled)
 5. A photocatalyticallyactive coated substrate as claimed in claim 1 wherein the coatedsubstrate has a visible light reflection measured on the coated side of15% or lower.
 6. A photocatalytically active coated substrate as claimedin claim 1 wherein the substrate comprises a glass substrate.
 7. Aphotocatalytically active coated substrate as claimed in claim 1 whereinthe coated substrate has an alkali metal ion-blocking under layerbetween the surface of the substrate and the photocatalytically activetitanium oxide coating.
 8. A photocatalytically active coated substrateas claimed in claim 7 wherein the alkali metal ion blocking under layeris a layer of silicon oxide.
 9. A photocatalytically active coatedsubstrate as claimed in claim 1 wherein the photocatalytically activetitanium oxide coating has a thickness of 30 nm or lower.
 10. (canceled)11. (canceled)
 12. A photocatalytically active coated substrate asclaimed in claim 1 wherein the coated surface of the substrate has astatic water contact angle of 20° or lower.
 13. A photocatalyticallyactive coated substrate as claimed in claim 1 wherein the coatedsubstrate has a haze of less than 1%.
 14. A photocatalytically activecoated substrate as claimed in claim 1 produced by a process as claimedin claim
 1. 15. A photocatalytically active coated substrate as claimedin claim 1 wherein the coated surface of the substrate is durable toabrasion, such that the coated surface remains photocatalytically activeafter it has been subjected to 300 strokes of the European standardabrasion test.
 16. A photocatalytically active coated substrate asclaimed in claim 15 wherein the coated surface remainsphotocatalytically active after it has been subjected to 500 strokes ofthe European standard abrasion test.
 17. A photocatalytically activecoated substrate as claimed in claim 16 wherein the coated surfaceremains photocatalytically active after it has been subjected to 1000strokes of the European standard abrasion test.
 18. A photocatalyticallyactive coated substrate as claimed in claim 16 wherein the haze of thecoated substrate is 2% or lower after being subjected to the Europeanabrasion test.
 19. A photocatalytically active coated substrate asclaimed in claim 1 wherein the coated surface of the substrate isdurable to humidity cycling such that the coated surface remainsphotocatalytically active after the coated substrate has been subjectedto 200 cycles of the humidity cycling test.
 20. A durablephotocatalytically active coated glass comprising a glass substratehaving a coating on one surface thereof, said coating comprising analkali metal ion-blocking under layer and an outer photocatalyticallyactive titanium oxide layer, wherein the coated surface of the substrateis durable to abrasion such that the coated surface remainsphotocatalytically active after it has been subjected to 300 strokes ofthe European standard abrasion test.
 21. A durable photocatalyticallyactive coated glass as claimed in claim 20 wherein the coated glass hasa visible light reflection measured on the coated side of 35% or lower,and wherein the photocatalytically active titanium oxide layer has athickness of 30 nm or lower.
 22. (canceled)
 23. A multiple glazing unitcomprising a first glazing pane of a coated substrate as claimed inclaim 1 in spaced, opposed relationship to a second glazing pane. 24.Laminated glass comprising a first glass ply of a coated glass asclaimed in claim 1, a polymer interlayer, and a second glass ply.